Various processes for the nitration of hydrocarbons have already been proposed. Of particular interest are processes for the nitration of propane, ethane and mixtures of these hydrocarbons. LHonore et al, U.S. Pat. No. 3,780,115, describes nitration of propane with nitrogen peroxide in the presence of oxygen, introduced in the form of air, under a pressure of 8 to 14 bars and at introduction temperatures of the reactants in the reaction zone on the order of 200.degree. to 240.degree. C.
Copending application Ser. No. 025,594, Mar. 30, 1979, now U.S. Pat. No. 4,260,838, relates to nitration of a mixture containing a substantial amount of propane. The reaction temperature and pressure, contact time and quantitative ratios among the nitrating agent, the mixture to be nitrated and the oxygenated gas are selected so that the nitration reaction is performed in the homogeneous gaseous phase. The mixture to be nitrated contains propane and one or more other alkanes having up to five carbon atoms in the molecule.
The conditions for nitration of ethane are the object of copending Ser. No. 094,153 of Nov. 14, 1979, now U.S. Pat. No. 4,313,010. According to this process the quantitative ratios of the various constituents of the reaction mixture, the reaction contact time and the reaction temperatures and pressures are selected and controlled so that nitration of the ethane takes place in a homogeneous gaseous phase, and as a function of the range of nitroparaffins expected to be obtained.
As in the previous processes for nitrating propane or propane base mixtures, the nitration reaction can be performed in the presence of an active agent carrying an easily transferable NO or NO.sub.2 group, such as 2-nitropropane or nitroethane, alone or in mixture, possibly recycled reaction product. These nitrations are also advantageously performed in the presence of a gas, inert in the reaction (hereinafter an "inert gas"), selected from nitrogen, carbon monoxide, carbon dioxide, hydrogen, methane, argon or a mixture of any of these gases.
For all these processes, the highest yields are obtained only by working with a gradual and regular heat regime, i.e. by controlling the temperature curve inside the reaction zone; this curve must be smooth, i.e. have a regular growth without inflection points. Such a heat regime can be obtained only by avoiding any racing of the reaction and the appearance of high temperatures at certain points of the reaction zone.